Vapor Deposition Electron Beam Current Control

ABSTRACT

Systems and methods are described that monitor electron beam current and voltage. The systems and methods react to fault conditions such as arcing experienced during evaporation and deposition processes to shutdown and protect associated power supply equipment. The systems and methods may provide online beam current control to provide stable operation of e-beam guns during heating and melting modes of operation.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. patent application Ser. No. 61/118,812, filedDec. 1, 2008, and entitled “Vapor Deposition Electron Beam CurrentControl”, the disclosure of which is incorporated by reference herein inits entirety as if set forth at length.

BACKGROUND

The disclosure relates generally to the field of vacuum deposition. Morespecifically, the disclosure relates to systems and methods forcontrolling electron beam filament current used in electron beamphysical vapor deposition for aircraft engine turbine blades andaccessories.

Today, vacuum deposition of thin films and coatings is evolving. This istrue of their processes, equipment, applications and markets.

Electron beam physical vapor deposition (PVD) is a material coatingtechnology where a coating, such as a metal, alloy, or ceramic ismelted, vaporized in a vacuum, and then deposited on a work piece. Thematerial to be deposited is converted to a vapor by physical means.Generally, the process deposits atoms or molecules one at a time. Sincethe process is performed in a vacuum, it is an environmentally friendlytechnology, suitable as a replacement for other coating processes inmany applications. The technology is capable of producing coatings for awide range of industrial applications.

PVD processes are atomistic where material vaporized from a solid orliquid source is transported as a vapor through a vacuum or low-pressureenvironment. When it contacts the work piece, it condenses. PVDprocesses are used to deposit films with thicknesses in the range of afew nanometers to thousands of nanometers, however, they can be used toform multilayer coatings, thick deposits and free-standing structures.

Vacuum evaporation is a PVD process where material from a thermalvaporization source reaches the substrate without collision with gasmolecules in the space between the source and substrate. The trajectoryof the vaporized material is in a line-of-sight.

The equipment used to generate a deposition environment is an integralpart of the process. The principal parts of the deposition system arethe deposition chamber, evaporation tools, fixtures (which hold theparts to be coated), and the vacuum pumping system (which removes gasesand vapors from the deposition chamber).

Generating a vacuum reduces the gas pressure so that vaporized atomshave a long mean-free path and do not nucleate in the vapor to formsoot. The vacuum also reduces the contamination level to the point thatthe desired film can be deposited. Fixtures hold the substrates to becoated and provide the motion, relative to the vaporization source. Thisis often necessary to give a uniform deposition over a large area, acomplex surface or over many substrates. The deposition chamber is sizedto contain the fixtures and provide room for accessories such asshutters, deposition rate monitors, heaters, etc. Proper design,construction, operation and maintenance are necessary to obtain areproducible product with high yield and desired product throughput.

The vaporization source is typically a high-energy, electron beam(e-beam) gun that is focused and rastered over the surface of the sourcematerial. E-beams are either hot-cathode or hot-filament thermionic gunswhere the electrons are generated by a hot filament of a hightemperature alloy such as tungsten. Beam electrons are generated byapplying a constant voltage, typically 20,000 to 120,000 V to thecathode. Electron emission from the cathode is increased by bombardingit with electrons from an electrically heated filament, typically at1000 V.

An axial, e-beam gun evaporation tool is shown in FIG. 1. During gunoperation, the cathode 101 is heated electrically by passing a currentthrough the filament 103 until it emits electrons 105 through thermionicemission. The electrons bombard the cathode 101, heating it and leadingto its own electron emission. Once the cathode 101 has begun to emitelectrons, electron bombardment from the cathode in combination withdirect electric current heating increases the cathode temperature,increases its electron current emission density, and results in a largeremitting surface than would be achieved through cathode operation only.

Gun systems use electromagnets located within the body of the gun forbeam focusing 107 and scanning 109. Beam scanning is an integral featurebecause it ensures rapid, uniform, controlled, atomistic evaporationfrom the largest possible target 111 surface.

FIG. 2 is a diagram of an exemplary process. The work piece 201 ismaintained at a specific temperature to ensure good adhesion of theevaporated material. Two 203, 205 of six e-beam guns are directed attrays containing crushed ceramic or graphite positioned adjacent to thework piece 201 for indirect heating. Up to four guns 207, 209, 211, 213are used for evaporation. FIG. 2 also shows the e-beam directing system221 and workpiece motion controller 223.

Specifying and controlling the maximum e-beam gun power for high or lowvacuum evaporation systems is problematic because of the uncertaintyinvolved in determining the magnitude of the various e-beam energylosses between generation of the beam and generation of the vapor. Theamount of e-beam energy actually available for material evaporationdepends upon the energy losses such as those experienced inside of a gundue to some fraction of the beam impinging on various portions of thegun, in the gas and vapor cloud 227 due to electron scatteringcollisions, from the evaporant material surface as a result of electronbackscattering, through conduction into the crucible containing the meltmaterial, from the radiating molten evaporant surface, and throughconvection caused by the gas jet blowing across the evaporant surface.With the above described energy losses and operating environment,problems related to electrical discharges manifest themselves from highvoltage in the presence of high vapor. The vapor may become ionizedresulting in interaction with the hot filament. An exemplary thresholdfor coaters is about 16 kV accelerating voltage: below this voltage thebeams do not penetrate the vapor very well. At operational voltages,arcing can occur. Arcing induces rapid, out of control filament current.Arcs caused by ionized vapors occur between the coater enclosure and thehigh-voltage circuits. Most often arcs occur in the guns and HV inputcircuits.

Pre-arc or non-arc interactions can occur between electron beam guns.This is evidenced by filament current fluctuations that may occurspontaneously or when the beam current is intentionally altered on anyone or more guns. Thermal process control may be lost during theseevents, with attendant substrate temperature excursions that mayadversely affect the applied coating characteristics (microstructure).

It is a challenge to ensure consistent production while offeringprotection for the e-beam gun support systems. It is therefore desirableto develop a system and method that protects gun subsystems in the eventof an arc within a gun or within the processing environment.

SUMMARY

Although there are various systems and methods that control filament andbeam current for electron beam guns used in vapor deposition, suchsystems and methods are not completely satisfactory. It would bedesirable to have systems and methods that monitor electron beam currentand voltage, and react to fault conditions such as arcing experiencedduring evaporation and deposition processes to shutdown and protectassociated power supply equipment.

Although arc down protection and arc recovery systems may be elements ofmulti-electron beam gun coating systems, and these functions may beprovided as a byproduct of the present method and apparatus, the presentdisclosure can provide enhanced thermal stability that is manifestedinto the process via electron beam gun filament current control. Thermalstability of the parts in the process is dependent upon input processparameters such as time, temperature, pressure, injected oxygenrelationships. These parameters influence the characteristics thatdetermine coating durability. Thus, attempts to control these parametersto improve stability are constrained by the desired coatingcharacteristics.

The disclosure provides online beam current control to provide stableoperation of e-beam guns during heating and melting modes of vapordeposition operation. Beam current supplied to each gun used in aprocess may be monitored. The measured current may be used in aclosed-loop feedback control to indirectly adjust beam current byadjusting filament current. Power supply protection may be provided forone or more e-beam guns having a shared, common beam high voltage powersupply.

One aspect of the disclosure provides methods for controlling a powersupply for an electron beam. Methods according to this aspect may startwith defining a high voltage level setpoint for a high voltage beampower supply output, defining a beam current setpoint, defining afilament current setpoint for a filament power supply output, monitoringthe high voltage beam power supply output voltage, monitoring currentsupplied to a cathode of the electron beam, and determining whether afault condition has occurred based on the high voltage beam power supplyoutput voltage and filament current.

Another aspect involves deriving a beam current value based on thefilament current and the high voltage beam power supply voltage.

Yet another aspect of the disclosure is an electron beam power supplysystem. Systems according to this aspect of the disclosure comprise ahigh voltage beam power supply having an output coupled to a cathode ofthe electron gun, a filament power supply having an output coupled to afilament of the electron gun, and a processor monitoring voltage appliedto the cathode and current applied to the filament, the processoroutputting control signals to the high voltage beam power supply and thefilament power supply wherein the control signals are responsive to thecathode voltage and the filament current and indicate fault conditionsexperienced by the electron beam.

Another aspect of the system involves a high voltage output levelsetpoint for predetermining a high voltage level, a filament powersupply current setpoint for predetermining a filament current level, anda beam current setpoint for predetermining a beam current level whereinthe beam current depends on the high voltage level and the filamentcurrent level.

Other objects and advantages of the methods and systems will becomeapparent to those skilled in the art after reading the detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary electron beam gun.

FIG. 2 is an exemplary cross-sectional view of a vapor depositionchamber.

FIG. 3 is an exemplary schematic of a control system.

FIG. 4 is an exemplary plot showing beam current and filament current atvarious values of high accelerating voltage.

FIG. 5 is a block diagram of an exemplary method according to theinvention.

FIG. 6 is an exemplary plot showing system operation during a faultcondition.

FIG. 7 is an exemplary schematic of the beam current regulator.

FIG. 8 is an exemplary plot of output signal beam current regulator 317for filament current control.

DETAILED DESCRIPTION

Embodiments are described with reference to the accompanying drawingfigures wherein like numbers represent like elements throughout.Further, it is to be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of “including,” “comprising,” or “having” andvariations thereof herein is meant to encompass the items listedthereafter and equivalents thereof as well as additional items. Theterms “mounted,” “connected,” and “coupled” are used broadly andencompass both direct and indirect mounting, connecting, and coupling.Further, “connected” and “coupled” are not restricted to physical ormechanical connections or couplings.

The disclosure is not limited to any particular software languagedescribed or implied in the figures. A variety of alternative softwarelanguages may be used for implementation. Some components and items areillustrated and described as if they were hardware elements, as iscommon practice within the art. However, various components in themethod and system may be implemented in software or hardware.

Embodiments provide systems and methods for controlling filament currentfor electron beam guns used in vapor deposition.

FIG. 3 is a schematic of a deposition control system 301. The exemplarysystem uses six e-beam guns. However, other numbers of guns may beemployed. The subscript _(x) identifies components and signal paths thatare associated with one gun (_(x)=1, 2, 3, . . . 6).

The control system 301 controls the beam current (I_BEAM) supplied toall guns 303 _(x) (I_BEAM_(x)) used in a process chamber 305 for PVD.The amount of beam current (I_BEAM_(x)) supplied to each gun 303 _(x)depends on the magnitude of the accelerating voltage and filamentcurrent (I_FILAMENT_(x)).

During vapor deposition, the chamber 305 vacuum, the properties of thematerial 307 being evaporated, electrical arcing, and other phenomenawhich occur inside the chamber 305 during processing all may affect gun303 _(x) filament current (I_FILAMENT_(x)). The simultaneous operationof several guns 303 _(x) sourced from a common high voltage (HV) powersupply affect gun 303 _(x) stability.

The common HV beam power supply system 308 includes an HV closed loopregulator 309, an SCR controller 311, an HV power supply 313, and an HVrectifier 315. The HV rectifier outputs an HVDC (direct current) to thegun cathodes (I_BEAM).

The system 301 uses a thyristor regulator 317 _(x) in the filamentcurrent path for each gun 303 _(x) in conjunction with closed-loopfeedback as part of the overall control. Each gun 303 _(x) has adedicated filament regulator system 321 _(x) that includes a beamcurrent regulator 317 _(x), an SCR controller 323 _(x), a filamentsupply 325 _(x), and a filament rectifier 327 _(x).

The beam current regulator 317 _(x) takes into account operationalfeatures of the controller (e.g., ENERPRO Corporation SCR series FCOG6100 (three phase firing board) or FCRO 2100 (single phasefiring/regulator board) controllers). The level of FCRO 2100 firingboard input command is from 0 up to +5 VDC; at the same time delay anglevaries from 180 to 0 degrees. Other devices with the appropriatespecifications can be used.

The system controls beam current (I_BEAM) in dependence on individualgun filament current (I_FILAMENT_(x)). Individual beam current(I_BEAM_(x)) feedback (V_FB_I_BEAM_GUN_(x)) provides an independent,on-line control for each gun 303 _(x) in use and provides stableoperation for different processing modes. Presetting filament current(I_FILAMENT_(x)) decreases the value of beam current deviation if thesystem terminates on a fault or HV arc which may occur in the chamberduring processing.

A processor 329 accepts feedback from the common HV output 339 (HV_FB),individual gun 303 _(x) beam current (V_FB_I_BEAM_GUN_(x)), and based ona control logic, outputs in response to the feedback signals thatcontrol the common HV power supply system 308 and each gun filamentregulator system 321 _(x). An HV voltage divider 343 provides a lowvoltage representation of the HV output 339 as feedback (HV_FB).

Each gun 303 _(x) comprises a cathode 331 _(x), an acceleratingelectrode 333 _(x) and a deflection coil 335 _(x). DC filament current319 _(x) (I_FILAMENT_(x)) heats the cathode 331 _(x) liberatingelectrons from its surface through thermionic emission.

The cathode 331 _(x) is coupled to a negative output of the HV rectifier315. The corresponding positive output of the HV rectifier 315 iscoupled to a chamber 305 ground terminal and an accelerating electrode333 _(x) ground terminal for each gun 303 _(x). When high voltage isapplied to each cathode 331 _(x), electrons are emitted and acceleratethrough the accelerating electrode 333 _(x) forming an electron beam 337_(x).

The deflection coil 335 _(x) rasters the electron beam 337 _(x) over anobject 307 for evaporation, or tray (not shown) for heating within inthe chamber 305. A discussion of raster control is beyond the scope ofthis disclosure.

Process parameters such as heating, and evaporant temperature and ratedepend upon the cathode and filament currents. Two plots of HV beamcurrent versus filament current corresponding to two different HVsetpoints are shown in FIG. 6. The Y axis shows the reading ofcontrollable value in arbitrary units. X axis—time. Unit of measurementis defined by the name of controllable value. Various controllablevalues are shown on one Y axis for better understanding of theirdependency in time: HV level 920; HV threshold comparator detector level922; arc comparator detector current level 924; beam current 926;filament current 928.

The HV feedback (HV_FB) is coupled to the HV regulator 309 and to an HVlevel comparator 345 input that is part of the processor 329. Beamcurrent sensors 347 _(x) produce beam current values(V_FB_I_BEAM_GUN_(x)) corresponding to each gun 303 _(x).

An arc detector 349 which is part of the processor 329 logic monitorsthe HV level. The system may enable beam current regulators of live gunsas soon as HV level reaches desired value (e.g., 90% of operatingvoltage HV). An arc detector 349 is used to detect over currentconditions which indicate shorting or HV arcing. Beam current(V_FB_I_BEAM_GUN_(x)) is also used as feedback for the beam currentregulator 317 _(x). The system compensates for electron beam 337 _(x)perturbations that occur by monitoring the variation of each gun's beamcurrent and voltage.

The power source for the SCR controller 311 and HV supply 313 is threephase alternating current (ac). Single phase ac is supplied to the SCRcontroller 323 _(x) and the filament supply 325 _(x).

The processor 329 analyzes the beam (I_BEAM) (HV_FB) and current(V_FB_I_BEAM_GUN_(x)) feedback. Processor 329 logic analyzes whether anover current condition exists. The processor 329 controls the common HVpower supply system 308 and each gun filament regulator system 321 _(x).

The processor 329 outputs on/off control commands to the common HV powersupply system 308 SCR controller 311 (HV_ON/OFF) and HV regulator 309(REG_HV_ON/OFF), and each gun filament regulator control system 321 _(x)beam current regulator 317 _(x) (REG_I_ON/OFF_(x)) and SCR controller323 _(x) (FILAMENT_ON/OFF_(x)) thereby turning on the common powersupply 308 and gun filament regulator systems 321 _(x) to energize orde-energize a gun.

A method of operation is shown in FIG. 5. After applying power to thesystem (step 505), a user adjusts the HV level setpoint 341, beamsetpoint 353, and filament setpoint 351 values (step 510).

The processor 329 reviews a list of permissives regarding possibleelectrical fault conditions for a determination of system availability(step 515). If no fault conditions are found (step 520), the gun systemis ready for operation (step 525). The invention turns on the HVregulator 309 (REG_HV_ON) and SCR controller 311 (HV_ON) (step 530) andgradually ramps-up (RAMPING_HV) the HV power supply output 339 via theregulator 309 to the HV level setpoint 341 (step 535).

The HV level setpoint 341 is used to define a desired HV level. The beamcurrent regulator 317 _(x) (REG_I_ON_(x)) and SCR controller 323 _(x)(FILAMENT_I_ON_(x)) are then turned on (step 540).

As soon as the predetermined HV level is reached, the beam currentregulator 317 _(x) output ramps-up (RAMPING_I_BEAM_(x)) to its setpoint351 (step 545). The system is in operation (step 550).

If a fault condition occurs (step 555), the arc detector 349 turns theprocessor 329 control outputs for the SCR regulator 311 (HV_OFF), HVregulator 309 (REG_HV_OFF), beam current regulator 317 x (REG_I_OFFx) toOFF (steps 560, 565), thereby de-energizing beam 308 power supplies andshutting down the evaporating tools for a finite period of time. If onegun arcs, all guns may be shutdown. The desired finite period of timedepends upon the properties of evaporating materials and may vary withinthe range of 0.2-5 seconds. The duration of such time is adjustedthrough the adjustment of the duration of disabling pulse (t pause 940after arc 942 in FIG. 6) that is generated by arc detector 349 as soonas arc is detected.

FIG. 6 is a plot of an arc transient and the system response over time.Beam current lags behind filament current because of cathode thermallag. Lines of filament current and beam current are shown in arbitraryunits since beam current value depends upon the gun design, cathodematerial, working value of accelerating voltage. Filament set point 351value depends upon these factors as well. Line 924 of ARC Level showsthe thresholds of arc current detector 349 response for each gun. Beamcurrent increase up to the preset value of arc level causes arc currentdetector 349 to generate control pulse (t pause after ARC) that disableshigh-voltage source and beam current regulators of all guns. Lines beamcurrent 926 and filament current 928 show beam current and gun filamentvalues. As soon as arc current detector 349 detects arcing it disableshigh-voltage source and beam current regulators of all guns. At the sametime beam current rapidly drops down to 0 and filament current decreasesto the preset value Fil Preset (see FIG. 4). Available filament currentkeeps hot state of cathode and protects cathode from abrupt variation ofits length at beam current enabling\disabling. As soon as HV levelreaches 90% of operating voltage HV threshold detector 345 allowsenabling of beam current regulators. Such control logic provides beamsetting (hit) to the initial position. Filament current increases at thepreset ramping and restores the working value of beam current.

When the processor 329 logic determines that the fault has ended and theevent is over (step 515) and operation can resume (step 520), the HVregulator 309 and SCR controller 311 are reset and turned on((REG_HV_ON), (HV ON)) (step 525). At the same time, a power supplyramping signal (RAMPING_HV) is output from the processor 329 thatramps-up the regulator 309 output to the HV setpoint 341 (step 530).

A filament on signal (FILAMENT_ON) is output from the processor 329 toSCR controller 323 _(x) and beam regulator 317 _(x) in addition to abeam current regulator 317 _(x) on signal (REG_I_ON_(x)) (step 535).

Processor 329 outputs the beam current regulator ramping signal(RAMPING_I_BEAM_(x)) when the beam voltage (HV_FB) reaches 80%-90% ofthe HV setpoint 341 (step 540). The system returns to operation (step545).

FIG. 7 is the beam current regulator 317 _(x) for each filamentregulator system 321 _(x). The filament current setpoint 351 allows forthe smooth ramp-up of filament current as soon as the SCR controller 323_(x) is turned on (FILAMENT_I_ON_(x)).

The beam current setpoint is set via potentiometer 353 or from anotheranalog device. A comparator 701 compares a desired beam current setpoint353 against actual beam current feedback (V_FB_I_BEAM_GUNx) and outputsa difference, or error signal. The error signal is amplified by a PI(proportional-integral) error amplifier 703. An analog adder 705 addsthe filament current setpoint 351 to the amplifier 703 output.

A limiter 707 limits the output of the adder 705 output preventingsaturation using the beam current setpoint 353 which is non-linearamplified 709 and added with the filament setpoint 351 which modifiesthe limit 707. FIG. 8 shows the output signal current regulator 317 forfilament current control.

A control device 711 (e.g., an electronic switch) outputs a signal inresponse to the beam regulator signal (REG_I_ON/OFF_(x)) that modifiesthe characteristics of the error amplifier 703 during arcing. As soon asarc occurs control device 711 disables the error amplifier 703. In thiscase output signal of regulator 317 corresponds to I Fil preset (seeFIG. 4)

Filament current presetting 713 sets I filament level via the regulator317 x when gun's filament is ON. Such filament level is adjusted foreach gun individually from filament set point 351. An adjustmentprocedure for finding set point 351 is: 1) preset HV set point 341 atoperating level HV; 2) preset set point I beam 353 to approximately 0mA; 3) increase slowly the filament set point 351 until beam current isabout 5 mA. The resultant value of filament set point 351 is fixed.

The disclosure facilitates operating mode of regulator 317 x and cathode331 x of a gun at beam current stabilization. The use of closed loopbeam current feedback in regulator 317 x which control of prefabricatedSCR controller 323 of filament current of each EB gun provides stableoperation of the system under various modes of evaporation anddeposition. Points I_FIL_PRESET A and B in FIG. 4 can be considered asinitial value of cathode filament at operating accelerating voltage 25kV (point A) or 18 kV (point B).

Points A, B show approximate values of filament current at 25 kV and 18kV accelerating voltage when beam current starts showing up.

The control is carried out in the following manner. See FIG. 3B, FIG. 4.Filament set point 351 sets initial current value of cathode filament(I_FIL_PRESET), that depends upon the preset operating voltage of HVsupply (see points A, B FIG. 4). Beam set point 353 sets signal levelfor Beam current close loop regulator 317 that transmits the command tothe input of SCR CONTROLLER 323 that provides control oversilicon-controlled rectifiers of Filament Supply 325. From the output ofFilament Supply 325 filament, gate voltage is supplied to filamentcurrent rectifier 327 that provides control over DC filament current 319of cathode 331 of gun 303. Signal of beam current-sensing device of thegun 303 is used as the signal of negative feedback in beam current closeloop regulator 317. Beam current value deviation from the preset valuecauses regulator 317 to generate filament control signal thatcompensates for beam current variation.

Although the disclosure herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. For example, the principles may be implemented inthe retrofit or other reengineering of existing systems used forexisting purposes. Physical and operational details of such existingsystems and purposes (e.g., component configurations, particularvoltages, particular currents, and the like) will influence or dictatedetails of any particular implementation. It is therefore to beunderstood that numerous modifications may be made to the illustrativeembodiments and that other arrangements may be devised without departingfrom the spirit and scope of the present invention as defined by theappended claims.

1. An electron beam power supply comprising: a beam power supply havingan output coupled to a cathode of an electron beam; a filament powersupply having an output coupled to a filament of the electron beam; anda processor monitoring voltage applied to said cathode and currentapplied to said filament, said processor outputting control signals tosaid high voltage beam power supply and said filament power supplywherein said control signals are responsive to said cathode voltage andsaid filament current and indicate fault conditions experienced by theelectron beam.
 2. The power supply according to claim 1 furthercomprising: a high voltage output level setpoint for predetermining ahigh voltage level; a filament power supply current setpoint forpredetermining a filament current level; and a beam current setpoint forpredetermining a beam current level wherein said beam current depends onsaid high voltage level and said filament current level.
 3. A method forcontrolling a power supply for an electron beam comprising: defining ahigh voltage level setpoint for a high voltage beam power supply output;defining a beam current setpoint; defining a filament current setpointfor a filament power supply output; monitoring said high voltage beampower supply output voltage; monitoring current supplied to a cathode ofthe electron beam; and determining whether a fault condition hasoccurred based on said high voltage beam power supply output voltage andsaid filament current.
 4. The method according to claim 3 furthercomprising terminating said high voltage beam power supply output andsaid filament power supply output upon a fault condition.
 5. The methodaccording to claim 4 further comprising deriving a beam current valuebased on said filament current and said high voltage beam power supplyvoltage.
 6. A deposition apparatus comprising: a chamber having aninterior; at least one electron gun positioned and oriented to direct anassociated electron beam within the deposition chamber; a control systemcoupled to the at least one electron gun having a beam power supplyhaving an output coupled to a cathode of an electron beam; a filamentpower supply having an output coupled to a filament of the electronbeam; and a processor monitoring voltage applied to said cathode andcurrent applied to said filament, said processor outputting controlsignals to said high voltage beam power supply and said filament powersupply wherein said control signals are responsive to said cathodevoltage and said filament current and indicate fault conditionsexperienced by the electron beam.
 7. The apparatus of claim 1 wherein:the at least one electron gun comprises a plurality of electron guns. 8.A deposition apparatus comprising: a chamber having an interior; aplurality of electron guns positioned and oriented to direct anassociated electron beam within the deposition chamber; and a controlsystem coupled to the pluralities of electron guns and having at least afirst thyristor regulator providing closed loop feedback of at least afirst gun of said at least one electron gun.
 9. The apparatus of claim 8wherein: the at least one thyristor regulator comprises a plurality ofcomprises a plurality of thyristor regulators providing closed loopfeedback of a respective plurality of electron guns of said at least oneelectron gun.
 10. The apparatus of claim 8 wherein: the at least onethyristor regulator comprises 4-8 thyristor regulators; and the at leastone electron gun consists of 4-8 electron guns, each controlled by atleast an associated one of the thyristor regulators.